1. Field of the Invention
The present invention relates to a method of measuring electrolytes in blood and urine by use of an electrode.
2. Description of the Prior Art
In case where electrolytes in a blood and urine are measured by use of an electrode, the measuring range is as follows for a blood:
______________________________________ Na.sup.+ -concentration 100 to 200 mmol/liter K.sup.+ -concentration 1.0 to 10.0 mmol/liter Cl.sup.- -concentration 80 to 200 mmol/liter ______________________________________
On the contrary, for a urine the measuring range is as follows:
______________________________________ Na.sup.+ -concentration 2 to 300 mmol/liter K.sup.+ -concentration 1 to 150 mmol/liter Cl.sup.- -concentration 2 to 300 mmol/liter ______________________________________
That is to say, the measuring range for a urine is considerably wide in comparison with that for a blood. A reason for this is that the metabolism of electrolytes is carried out in a remarkably narrow range for a blood and a slightest change of concentration exhibits a physiological activity while for a urine a quantity of salts and water ingested is directly reflected in the quantity thereof excreted, thereby remarkably changing the concentration of electrolytes.
Accordingly, in a case where a blood and a urine are measured in an apparatus for measuring electrolytes by use of an electrode, calibrating solutions (Low standard solution, High standard solution) for a blood and a urine are separately prepared and calibrating points for the calibrating solution for a blood are determined in the measuring range for a blood, thereby improving the accuracy in the measurement of a blood, while calibrating points for the calibrating solution for a urine are widely taken, thereby taking a measurement in as wide a range as possible. In this case, for example the following two kinds of calibrating solution have been used:
Calibrating solutions for a blood
______________________________________ Low High ______________________________________ Na.sup.+ 120 mmol/liter 160 mmol/liter K.sup.+ 4.0 mmol/liter 6.0 mmol/liter Cl.sup.- 100 mmol/liter 140 mmol/liter ______________________________________
Calibrating solutions for a urine
______________________________________ Low High ______________________________________ Na.sup.+ 80 mmol/liter 200 mmol/liter K.sup.+ 40 mmol/liter 7 mmol/liter Cl.sup.- 80 mmol/liter 200 mmol/liter ______________________________________
In addition, it has been known that the same one calibrating solution is used in either case where the sample to be measured is a blood or a urine to carry out the measurement with a one-point calibration by taking calibrating points of the calibrating solution widely. In this measuring method for example the following calibrating solution is used:
______________________________________ Low High ______________________________________ Na.sup.+ 130 mmol/liter 60 mmol/liter K.sup.+ 4 mmol/liter 20 mmol/liter Cl.sup.- 116 mmol/liter 71 mmol/liter ______________________________________
Besides, in a measurement of electrolytes by the ion-electrode method the activity of electrolytes is measured, so that it is necessary for the accurate measurement of the activity that the ion-strength is constant. And, an ion-electrode itself is influenced by pH according to circumstances. Accordingly, in the measurement of a blood or a urine the ion-strength of the blood is nearly constant and also pH is in a range of 7 to 9, so that no problem occurs even though it is measured as it is. However, the urine greatly fluctuates in ion-strength and also pH is remarkably low to an extent of 4 to 6, so that it has been usually diluted with a diluent containing a buffer agent such as magnesium acetate and other support salts and a tris-boric acid system, to make the ion-strength nearly constant, and pH has been adjusted and then the measurement has been carried out.
In the above described conventional measuring method, in the case where the calibrating solution for the exclusive use of the blood and the urine is used, respectively, a high accuracy of measurement can be maintained for the blood and the urine, respectively. However, problems have occurred in that it is necessary to prepare two kinds of calibrating solution and in the case where the sample to be measured is changed from the blood to the urine, it is necessary to change the calibrating solution at the same time and to provide a measuring apparatus of an ion-electrode with a change-over valve, a line for the blood and a line for the urine, whereby the measuring apparatus is large-sized and its operation is complicated.
The measuring method in which the same one calibrating solution is used for both the blood and the urine does not require the selection of the calibrating solution depending on the sample to be measured, making it easy to prepare the calibrating solution, and being capable of simplifying the measuring apparatus in construction. However, since the calibrating points of the calibrating solution are widened because of the measuring range of the urine, problems have occurred in that the accuracy of measurement for the blood is lowered and the linearity is lost in a lower-concentration range and a higher-concentration range. That is to say the measurement is unstabilized in view of accuracy of measurement for the urine, too.